How this calculator works
Uncompressed audio samples the waveform at a fixed rate and stores each sample in a fixed number of bits, separately for each channel. The bitrate is therefore sample rate times bit depth times channels: 44,100 samples per second at 16 bits over two channels is 1,411,200 bits per second. Multiplying by the length in seconds and dividing by eight gives bytes. A four-minute stereo track at CD quality is about 42.3 megabytes. Compressed formats such as MP3 and AAC store a smaller file at a chosen bitrate, so their size is the bitrate times the length instead.
Formula
bitrate (bit/s) = sample rate (Hz) x bit depth (bits) x channels. file size (bytes) = bitrate x length (s) / 8. length (s) = file size x 8 / bitrate. required bitrate = file size x 8 / length.
Worked example
A four-minute stereo track at 44.1 kHz and 16 bits: 44,100 x 16 x 2 = 1,411,200 bit/s. Four minutes is 240 seconds, so the file is 1,411,200 x 240 / 8 = 42,336,000 bytes, about 42.34 MB or 40.37 MiB. Doubling the sample rate to 88.2 kHz would double the size, and recording in 24-bit adds 50 percent over 16-bit at the same rate.
Advertisement
Frequently asked questions
Why is the file larger than the bitrate times the length?
The calculation gives the raw audio payload. Real files add headers, metadata, cue points and container overhead, often a few kilobytes per file. For a long recording the difference is negligible, but a folder of short clips carries more overhead in total.
Does a higher sample rate improve quality?
It extends the highest frequency that can be recorded, up to half the sample rate. 44.1 kHz captures up to about 22 kHz, which covers most of human hearing. Higher rates help when the audio will be processed or slowed down, but they cost storage in direct proportion.
What is the difference between MB and MiB here?
One decimal megabyte is 1,000,000 bytes and one mebibyte is 1,048,576 bytes. Recording software often reports binary units, so a file listed as 42.34 MB on this page can appear as 40.37 MiB in a file manager. Both describe the same bytes.
How do I work out a compressed file size?
Use the bitrate mode with the encoded bitrate and the length. A 320 kbit/s MP3 uses 320,000 bits per second, so four minutes is 9.6 MB. Variable bitrate files vary around that figure and cannot be predicted exactly from the header alone.